As a technique for connecting a resin-made tube by using an inner ring, for example, the technique disclosed in Patent Literature 1 is known.
The configuration disclosed in Patent Literature 1 includes: a tubular screwing portion which is disposed in a pipe joint in a state where an external thread is formed on the outer circumference; an inner ring in which the inner circumferential portion is formed as a fluid passage, and an annular large-diameter portion is raised on the radially outward side, and which is used for fixing a pipe; and a union nut on which an internal thread to be screwed with the external thread is formed.
When a tube is to be connected to the pipe joint, the inner ring is first press-inserted into an end portion of the tube from an opening of the tube, and the end portion of the tube is flared and deformed by the annular large-diameter portion.
Next, the tube which is flared and deformed, and which has the inner ring is inserted into the tubular screwing portion.
Next, the internal thread of the union nut is screwed with the external thread of the tubular screwing portion.
Then, the union nut is screw-advanced, and this screw advancement causes the union nut to press the tube having the inner ring in the axial direction, thereby performing the connection of the tube.
The press insertion of the inner ring into the end portion of the tube from the opening of the tube is performed by using a dedicated press-insertion jig (press-insertion device).
The forced press insertion which is performed by using a press-insertion jig (press-insertion device) is disclosed in, for example, Patent Literature 2 and Patent Literature 3.
In the configurations disclosed in Patent Literature 2 and Patent Literature 3, an inner ring is fitted to an pushing mechanism, a tube is fixed to a clamp jig so that an end portion of the tube is projected, and the inner ring is pressed in the axial direction by operating the pushing mechanism, to be press-inserted into the end portion of the tube from an opening of the tube.
In the press-insertion jig (press-insertion device), in order to allow the tube and the inner ring to be press-inserted straightly and tightly to each other, the relative positions and directions of the axes of the clamp jig and the pushing mechanism are accurately coincident with each other.
When the tube and the inner ring are press-inserted to each other while their axes X, P are not inclined to each other, the following configuration is attained.
As shown in FIG. 12, the inner circumferential surface of the end portion 4C of the tube 4, and the outer circumferential portion 3G of the inner ring 3 are annularly press-contacted with each other in critical places as illustrated by the cross hatchings. Therefore, an annular sealed state which is uninterrupted (without a missing annular part) is configured in all of the critical places.
A case where the conventional inner ring 3 shown in FIG. 11 is press-inserted into the end portion 4C of the tube 4 while their axes X, P are not inclined to each other and are coincident with each other will be further described with reference to FIG. 12. The following configuration is attained.
In the conventional inner ring 3 shown in FIG. 11, first, a flared portion 3f having an outer-circumferential flared surface 3a which is tip-contracted in a conical manner, and a maximum-diameter portion 3b is formed, an outer circumferential portion 3c which is tip-expanded in a conical manner is formed from the maximum-diameter portion 3b of the flared portion 3f, and a linear trunk outer-circumferential portion 3d having the same diameter is formed from the outer-circumferential portion 3c. 
When the inner ring 3 is press-inserted into the end portion 4C of the tube 4,
an annular first press-contact portion a1 shown in FIG. 12 is configured in a tip-end front portion in the outer-circumferential flared surface 3a, 
an annular second press-contact portion a2 shown in FIG. 12 is configured in a range from a position between the outer-circumferential flared surface 3a and the maximum-diameter portion 3b, to the maximum-diameter portion 3b, 
an annular third press-contact portion a3 shown in FIG. 12 is configured in a range from the maximum-diameter portion 3b to a position between the maximum-diameter portion 3b and the tip-expanded outer-circumferential portion 3c, 
a fourth press-contact portion a4 is formed between the tip-expanded outer-circumferential portion 3c and the trunk outer-circumferential portion 3d, and
an annular fifth press-contact portion a5 shown in FIG. 10 is configured in a large part of the trunk outer-circumferential portion 3d. 
When the annular first to fifth press-contact portions a1 to a5 are configured as described above, the boundary between the end portion 4C of the tube 4 and the inner ring 3 is satisfactorily sealed, no fluid leakage occurs, and no space into which a fluid can enter is formed between the end portion 4C and the inner ring 3.
In an actual press-inserting work, however, there is a case where the ideal state where the press insertion of the tube and the inner ring is performed while there axes are not inclined to each other and are coincident with each other is not attained as described above. The case where the ideal state is not attained has intensively studied, and it is found that the case is caused mainly by following reasons (1) to (3).
(1) The resin-made tube is fixed to the clamp jig, and an end portion of the tube is projected. The inner ring is forcedly pressed by the pushing mechanism to be press-inserted into the projected end portion of the tube. During the press-insertion, therefore, the projected end portion of the tube is sometimes somewhat bent and deformed. When such bending deformation occurs, there is a case where the insertion is performed while the axis of the inner ring is slightly inclined to that of the end portion of the tube.
(2) An end surface of a tube which is manually cut in the site is not always cut perpendicularly to the axis of the tube, and sometimes cut in a state where the end face is slightly inclined.
When the inner ring is pressed against and press-inserted into the tube in which the end surface is slightly inclined, a time difference is produced so that the press insertion is sequentially performed with starting from a portion which is most axially projected in the tube.
Therefore, the friction force due to the press insertion is not applied simultaneously and uniformly to the whole circumference of the tube, but sequentially applied while being biased in the circumferential direction. Similarly with (1) above, there is a case where the insertion is performed while the axis of the inner ring is slightly inclined to that of the end portion of the tube.
(3) The resin-made tube is continuously extrusion-molded and then delivered in a state where the tube is wound around a cable core. The wound tube is curled, and therefore corrected so as to have a straight shape. However, it is difficult to completely remove the curl, and it is often that the tube is slightly axially bent.
Depending on the degree of the curl, when the curl is large, there is a case where the inner ring is not inserted while that axis of inner ring is straight to that of the end portion of the tube, but press-inserted while being slightly inclined.
Because of these reasons, the axis of the tube is inclined to that of the inner ring. The inclination of the tube is small or about 1 degree at the most in terms of the inclination of the axes. When the axes are inclined to each other, however, there arise the following problems.
As shown in FIG. 13, namely, the second to fifth press-contact portions a2 to a5 exhibit a press-contacting situation similar to that shown in FIG. 12, but the first press-contact portion a1 is formed as a narrow strip-shaped region in a tip end portion of the inner ring 3 where the rigidity of the tube 4 acts in the outer-circumferential flared surface 3a of a conical surface, and diameter reduction and deformation easily occur.
While the maximum-diameter portion 3b of the inner ring 3 is press-contacted with the inner circumferential surface 4A of the tube 4, the end portion 4C of the tube 4 is inclined to the axis X with starting from the press-contact portion. Therefore, the narrow first press-contact portion a1 is not formed into an annular shape, and is intermittent in the circumferential direction, and a surface-pressure reduced portion n or a non-contact portion n is produced.
When the surface-pressure reduced portion n or the non-contact portion n is produced, the fluid is caused by the capillary action to penetrate from the place formed as the surface-pressure reduced portion n or the non-contact portion n into a gap portion k between the outer-circumferential flared surface 3a and a tip-contracted press-contact portion 4a which is obtained by enlargedly deforming the tube 4. The higher the permeability of the fluid, the higher the penetration degree. There is a possibility that the penetration reaches to the vicinity of the maximum-diameter portion 3b. 
The existence of the surface-pressure reduced portion n or the non-contact portion n can be known from the presence or absence of a flaw detection penetrant which, after the inner ring 3 is press-inserted into the tube 4, and they are impregnated in the flaw detection penetrant for a given time period, penetrates between the inner ring 3 and the tube 4.
When the fluid penetrates to the gap portion k (see FIG. 13), there arise the following defects.
Even when the interiors of the tube 4 and the pipe joint are washed and then a next fluid is flown, the former old fluid remains in the gap portion k, and oozes out from the surface-pressure reduced portion n or the non-contact portion n, and is mixed with the replaced new fluid. Therefore, defects such as that the purity of the new fluid is lowered, that the new fluid is modified, and that, in order to prevent as far as possible the mixture from occurring, a lot of time, washing fluid, and replacement fluid are consumed in washing and replacement are caused.